Boy Scout Troop 324 is planning to go hiking for 1 day. There are 12 boys in the troop, and they will be accompanied by 3 scout leaders. Each person will need at least 3 bottles of water that day. What is the minimum number of bottles of water needed for the trip?
The minimum total amount of water will be achieved when each person drinks the minimum amount of water. This is 3 bottles per person. There are 12 boys and 3 leaders for a total of 15 people. Thus, the minimum amount of water needed is $15 \cdot 3 = \boxed{45}$ bottles.